#include <linux/preempt.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
-#include <linux/slab.h>
#include <linux/smp.h>
+#include <linux/delay.h>
#include <linux/srcu.h>
+static int init_srcu_struct_fields(struct srcu_struct *sp)
+{
+ sp->completed = 0;
+ mutex_init(&sp->mutex);
+ sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
+ return sp->per_cpu_ref ? 0 : -ENOMEM;
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int __init_srcu_struct(struct srcu_struct *sp, const char *name,
+ struct lock_class_key *key)
+{
+ /* Don't re-initialize a lock while it is held. */
+ debug_check_no_locks_freed((void *)sp, sizeof(*sp));
+ lockdep_init_map(&sp->dep_map, name, key, 0);
+ return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(__init_srcu_struct);
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
/**
* init_srcu_struct - initialize a sleep-RCU structure
* @sp: structure to initialize.
*/
int init_srcu_struct(struct srcu_struct *sp)
{
- sp->completed = 0;
- mutex_init(&sp->mutex);
- sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
- return (sp->per_cpu_ref ? 0 : -ENOMEM);
+ return init_srcu_struct_fields(sp);
}
+EXPORT_SYMBOL_GPL(init_srcu_struct);
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/*
* srcu_readers_active_idx -- returns approximate number of readers
free_percpu(sp->per_cpu_ref);
sp->per_cpu_ref = NULL;
}
+EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
-/**
- * srcu_read_lock - register a new reader for an SRCU-protected structure.
- * @sp: srcu_struct in which to register the new reader.
- *
+/*
* Counts the new reader in the appropriate per-CPU element of the
* srcu_struct. Must be called from process context.
* Returns an index that must be passed to the matching srcu_read_unlock().
*/
-int srcu_read_lock(struct srcu_struct *sp)
+int __srcu_read_lock(struct srcu_struct *sp)
{
int idx;
preempt_enable();
return idx;
}
+EXPORT_SYMBOL_GPL(__srcu_read_lock);
-/**
- * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
- * @sp: srcu_struct in which to unregister the old reader.
- * @idx: return value from corresponding srcu_read_lock().
- *
+/*
* Removes the count for the old reader from the appropriate per-CPU
* element of the srcu_struct. Note that this may well be a different
* CPU than that which was incremented by the corresponding srcu_read_lock().
* Must be called from process context.
*/
-void srcu_read_unlock(struct srcu_struct *sp, int idx)
+void __srcu_read_unlock(struct srcu_struct *sp, int idx)
{
preempt_disable();
srcu_barrier(); /* ensure compiler won't misorder critical section. */
per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]--;
preempt_enable();
}
+EXPORT_SYMBOL_GPL(__srcu_read_unlock);
-/**
- * synchronize_srcu - wait for prior SRCU read-side critical-section completion
- * @sp: srcu_struct with which to synchronize.
- *
- * Flip the completed counter, and wait for the old count to drain to zero.
- * As with classic RCU, the updater must use some separate means of
- * synchronizing concurrent updates. Can block; must be called from
- * process context.
- *
- * Note that it is illegal to call synchornize_srcu() from the corresponding
- * SRCU read-side critical section; doing so will result in deadlock.
- * However, it is perfectly legal to call synchronize_srcu() on one
- * srcu_struct from some other srcu_struct's read-side critical section.
+/*
+ * We use an adaptive strategy for synchronize_srcu() and especially for
+ * synchronize_srcu_expedited(). We spin for a fixed time period
+ * (defined below) to allow SRCU readers to exit their read-side critical
+ * sections. If there are still some readers after 10 microseconds,
+ * we repeatedly block for 1-millisecond time periods. This approach
+ * has done well in testing, so there is no need for a config parameter.
*/
-void synchronize_srcu(struct srcu_struct *sp)
+#define SYNCHRONIZE_SRCU_READER_DELAY 10
+
+/*
+ * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
+ */
+static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
{
int idx;
return;
}
- synchronize_sched(); /* Force memory barrier on all CPUs. */
+ sync_func(); /* Force memory barrier on all CPUs. */
/*
* The preceding synchronize_sched() ensures that any CPU that
idx = sp->completed & 0x1;
sp->completed++;
- synchronize_sched(); /* Force memory barrier on all CPUs. */
+ sync_func(); /* Force memory barrier on all CPUs. */
/*
* At this point, because of the preceding synchronize_sched(),
* all srcu_read_lock() calls using the old counters have completed.
* Their corresponding critical sections might well be still
* executing, but the srcu_read_lock() primitives themselves
- * will have finished executing.
+ * will have finished executing. We initially give readers
+ * an arbitrarily chosen 10 microseconds to get out of their
+ * SRCU read-side critical sections, then loop waiting 1/HZ
+ * seconds per iteration. The 10-microsecond value has done
+ * very well in testing.
*/
+ if (srcu_readers_active_idx(sp, idx))
+ udelay(SYNCHRONIZE_SRCU_READER_DELAY);
while (srcu_readers_active_idx(sp, idx))
schedule_timeout_interruptible(1);
- synchronize_sched(); /* Force memory barrier on all CPUs. */
+ sync_func(); /* Force memory barrier on all CPUs. */
/*
* The preceding synchronize_sched() forces all srcu_read_unlock()
mutex_unlock(&sp->mutex);
}
+/**
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Flip the completed counter, and wait for the old count to drain to zero.
+ * As with classic RCU, the updater must use some separate means of
+ * synchronizing concurrent updates. Can block; must be called from
+ * process context.
+ *
+ * Note that it is illegal to call synchronize_srcu() from the corresponding
+ * SRCU read-side critical section; doing so will result in deadlock.
+ * However, it is perfectly legal to call synchronize_srcu() on one
+ * srcu_struct from some other srcu_struct's read-side critical section.
+ */
+void synchronize_srcu(struct srcu_struct *sp)
+{
+ __synchronize_srcu(sp, synchronize_sched);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu);
+
+/**
+ * synchronize_srcu_expedited - like synchronize_srcu, but less patient
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Flip the completed counter, and wait for the old count to drain to zero.
+ * As with classic RCU, the updater must use some separate means of
+ * synchronizing concurrent updates. Can block; must be called from
+ * process context.
+ *
+ * Note that it is illegal to call synchronize_srcu_expedited()
+ * from the corresponding SRCU read-side critical section; doing so
+ * will result in deadlock. However, it is perfectly legal to call
+ * synchronize_srcu_expedited() on one srcu_struct from some other
+ * srcu_struct's read-side critical section.
+ */
+void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+ __synchronize_srcu(sp, synchronize_sched_expedited);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
/**
* srcu_batches_completed - return batches completed.
* @sp: srcu_struct on which to report batch completion.
{
return sp->completed;
}
-
-EXPORT_SYMBOL_GPL(init_srcu_struct);
-EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
-EXPORT_SYMBOL_GPL(srcu_read_lock);
-EXPORT_SYMBOL_GPL(srcu_read_unlock);
-EXPORT_SYMBOL_GPL(synchronize_srcu);
EXPORT_SYMBOL_GPL(srcu_batches_completed);
Code Review / linux-2.6.git / blobdiff